In general, permanent waving of human hair is achieved by chemically breaking the sulfur-to-sulfur or disulfide cystine bonds occurring naturally in human hair and then reforming the cystine bonds while the hair is wrapped or curled on rods. The sulfur-to-sulfur cystine bonds in human hair maintain the hair in a naturally straight or curly configuration and, in order to permanently reshape the hair into a lasting, different configuration, a significant percentage of the sulfur-to-sulfur bonds must be broken and then reestablished after the hair is reconfigured in a desired position, such as wrapped around a suitable mandrel or roller. In general, the sulfur-to-sulfur cystine bonds are broken with a waving lotion composition, containing a reducing agent, and after the hair is wound into a curl formation around a rod or roller, the sulfur-to-sulfur cystine bonds are relinked or reestablished while the hair is in the curl formation by contacting the hair, in the new formation, with an oxidizing agent, such as hydrogen peroxide or a water-soluble bromate.
As set forth in U.S. Pat. No. 5,116,608 others have used a reducing agent composition that is a quaternary ammoniomercaptan, such as thiocholine, or its salts, and discloses that the addition of a second reducing agent, such as thioglycolic acid, cysteamine or cysteine, is not detrimental to the reducing action of the ammoniomercaptan. Also an N-acylcysteamine HSCH.sub.2 CH.sub.2 NH--COR(R=2-10 C alkyl), as a hair reducing compound, has been used together with another reducing agent selected from the group consisting of cysteine, acidic sodium hyposulfite, sodium sulfite, thioglycerol and thiolactic acid, as disclosed in Japanese Patent HEI 2-53714. Miyazaki et al. U.S. Pat. No. 4,139,610 discloses a combination of cysteine and N-acetylcysteine. Nandagiri et al. U.S. Pat. No. 5,260,054 discloses cysteamine as a reducing agent, and Showa Japanese Patent 57062217 (Application No. 55-136857) discloses cysteamine together with an optional second reducing agent. U.S. Pat. No. 5,165,427 discloses cysteinamide as a reducing agent. U.S. Pat. No. 5,223,252 discloses a combination of a thioglycolate and cysteine at a pH of 7.5 to 9.5. U.S. Pat. No. 5,332,570 discloses a combination of cysteamine hydrochloride and a thio compound, such as monoethanolamine thioglycolate (MEATG), at a weight ratio of about 40:60, together with isoascorbic acid.
The reducing action of mercaptans on keratin is due mostly to the dissociated form of the thiol groups, the thiolate anion. "Acid" permanent waves sufficiently curl hair at a lower pH compared to alkaline permanent waves, e.g., at about 8.0 and above, because the waving agents in these permanent waves have low pKa values and thus exist predominantly in dissociated (thiolate) form at a pH approaching neutral. Hence, the pKa value shows that some mercaptans are efficient at high pH while others with a low pKa value and high ionization constant are efficient at lower pH values. Therefore, it is generally understood, by those skilled in the art, that acceptable waving efficiency is usually obtained by working near the pKa of the active reducing agent. For example, it is well known that the alkaline salts of thioglycolic acid, e.g., the ammonium salt of thioglycolic acid (pKa=10.4) has acceptable waving efficiency only if the pH of solution exceeds 9, see Zviak, Charles, The Science of Hair Care, Permanent Waving and Hair Straightening, p. 191, 1986; while amides such as thioglycolamide (pKa=8.4), and esters such as glycerol thioglycolate (pKa=7.8) give acceptable waving efficiency at neutral and even slightly acid pH.
Different reducing agents are effective to break the cystine bonds that crosslink human hair protein at the different pH values. Generally speaking, the acid permanent wave compositions having a lower pH include reducing agents such as bisulfites, e.g., ammonium bisulfite, or glycerol monothioglycolate, capable of breaking the sulfur-to-sulfur cystine bonds within lower pH ranges, whereas the alkaline permanent wave compositions, having a pH in the range of about 7.5 to 9.5, require an alkaline salt of thioglycolic acid so that the alkali can penetrate and swell the hair shaft for easier penetration of the reducing agent in order to break the sulfur-to-sulfur cystine bonds.
The use of diammonium dithiodiglycolate in acid or alkaline permanent wave lotions allows greater flexibility in processing time because it minimizes the possibility of overprocessing. This is due to the fact that the reaction of thioglycolic acid (TGA) with hair keratin is an equilibrium process. Thus by including diammonium dithiodiglycolate (oxidized TGA) in the wave lotion, the rate of the reaction of the thioglycolic acid with hair keratin is decreased and prevented from going to completion.
It is theorized that somewhere in the range of about 20% to about 60% of the natural sulfur-to-sulfur cystine bonds in the hair shafts should be broken in order to give the hair the capability of being reshaped to any desired shape, such as curled around a rod or roller, or straightened, and capable of retaining this new shape. If too few of the sulfur-to-sulfur bonds are broken, the natural or normal configuration of the hair will predominate, causing the hair to retain its previous shape. This is because the predominant prior or natural bonds in the hair dictate that the hair will remain in the old configuration or shape. Hydrogen bonds are physically broken when wet hair is stretched and wrapped around a roller. When the hair is dried, the hydrogen bonds are reformed in a curled position or shape. While the hydrogen bonds aid to maintain the hair in the new configuration, the sulfur-to-sulfur cystine bonds are much stronger and, to a much greater extent than the hydrogen bonds, control the efficacy of the permanent wave.
In order to successfully provide a satisfactory permanent wave in the hair, the sulfur-to-sulfur cystine bonds reformed in the hair in the new or curled configuration, when the hair is later oxidized with the neutralizing agent, should be stronger than the prior or natural cystine hair bonds. It is desired, therefore, when permanent waving, that enough new bonds in a new hair configuration are formed during permanent waving to outnumber the old bonds remaining that tend to form the hair in its prior or natural configuration, whether it be straight or naturally curled.
Since damaged hair already has a significant number of the sulfur-to-sulfur cystine bonds broken due to some chemical, mechanical or environmental abuse, particularly the chemical abuses, such as bleaching, tinting or frosting, it is difficult to determine what length of time, and what reducing agent concentration to apply to the hair to provide the hair with the proper number of sulfur-to-sulfur bonds remaining after the reducing agent treatment. Significantly damaged hair, such as bleached hair, may require a reducing agent lotion application for a period of only about 5 minutes whereas normal hair, not significantly damaged, may require the reducing agent lotion for a period of approximately 20 minutes under the same reducing agent concentration and temperature in order to result in both the damaged and normal hair having approximately the same curl configuration. Ideally, after the reducing agent treatment, every one of the hair shafts treated will contain the same ratio of broken to unbroken bonds so that this same ratio can be reestablished in each hair shaft when the hair is in the new configuration to provide a consistent strong curl over the entire head of hair.
Generally, the reducing agent lotion is applied to the hair by first shampooing the hair and then applying the reducing agent lotion to the hair, either before or after the hair is wrapped around suitable rollers. Since it is not possible for even the experienced permanent wave applier to accurately determine visually the extent of damage to the hair in order to have a better idea of how long the reducing agent should be in contact with the hair, it is necessary to take a "test curl" so that after a predetermined amount of time, for example 10 minutes, a first roller is removed from the hair and the curl is felt and stretched in an attempt to determine if the curl formation is strong enough. Once it is determined that the reducing agent has been in contact with the hair for a sufficient time period, the hair is rinsed thoroughly with water while still on the rollers or rods and, while the hair remains on the rollers or rods, a neutralizing agent, or neutralizing solution, is applied to oxidize and reform the sulfur-to-sulfur bonds while the hair is in the new, rolled configuration. The neutralizing agent contains an oxidizing agent, such as hydrogen peroxide or a bromate salt, in order to reestablish the sulfur-to-sulfur bonds to leave the hair in a relatively permanent, e.g., 2-4 months, new configuration. The rods are removed, before or after rinsing out the neutralizing agent.
When the reducing agent lotion is applied to sections of the head prior to rolling that portion of the hair onto the rods it is called a lotion wrap whereas when the hair is rolled on the rods or rollers first and then the lotion applied onto all of the hair after rolling, this is called a water wrap. The timing for the reducing agent to be in contact with the hair for a lotion wrap is begun from the time that all rods are on the head, and the timing for a water wrap begins from the time that the lotion application is completed. The capability of using a water wrap is clearly more desirable since the lotion is applied to the entire head of hair all at once in a short period of time and can be rinsed from the hair all at once to provide a more uniform reducing agent contact time for all of the hair.
Other prior art patents directed to permanent waving compositions intended to permanently wave both normal and damaged hair are found in the Klemm et al. U.S. Pat. No. 4,273,143; and Cannel et al. U.S. Pat. No. 4,301,820. Japanese Patent No. 57-212110 appears to be directed to a post-permanent treatment containing glycerine to give hair sheen and luster.